Patent Application
20110147563
This application claims priority of Swiss patent application no. 0059/10 filed Dec. 20, 2009 and German patent application number 10 2009 059 021.8 filed Dec. 21, 2009, the entire disclosures of which are incorporated by reference herein.
The present invention relates to a ceiling mount for a surgical microscope, including at least two load-bearing sections joined together by a damping interface, said interface including at least two damping layers which are made of damping material and are separated from each other by a bracket plate made of non-damping material.
The use of ceiling mounts involves the problem of vibrations or vibration feedback which may occur, on the one hand, when the ceiling vibrates and/or when the instrument (e.g. a microscope) is touched or moved and, on the other hand, as a result of operation or movement of control consoles which are associated with the instrument and also suspended from the ceiling mount. Ceiling vibrations generally occur unpredictably and may be caused by various sources, such as compressors, air-conditioning systems, engines, and also seismic vibrations, or vibrations caused by transport of masses, such as occur during passage of a heavy vehicle thereabove, or during landing of a helicopter on the roof, or the like.
In the case of floor stands, contact-induced vibrations can be controlled, for example, by support feet made of mechanically damping materials, whereas in the case of ceiling mounts, there is a phenomenon which cannot be easily eliminated in a similar fashion, as will be described below. The ceiling of an operating room generally vibrates at different frequencies and amplitudes with respect to the floor. Therefore, it is insufficient to merely damp natural vibrations excited by contact or movement. The inventor has recognized that when a ceiling mount is used, it is required to damp not only the natural vibration of the mount, but also the vibration excited by the ceiling itself. In the prior art, it is known to provide a damping interface between the building element and the instrument. The effect of the interface is that vibration processes occurring before and behind it are different and ideally cancel each other out. The arrangement of the damping layers at horizontal interfaces has been described and implemented. These approaches aimed at the damping of natural vibrations. Damping of vibrations excited by the ceiling has not yet been described.
European Patent EP 1 067 419 B1 discloses a damped swing arm on a ceiling mount, in which a damping interface is provided between sections of a support arm which are pivotable relative to each other. The interface includes at least two identical damping layers separated by a non-damping layer. The rigid and elastic layers form a kind of sandwich element. The housing of this sandwich element is rigidly joined to the first section of the support arm, and the non-damping layer is rigidly joined to the second section of the support arm. The damping layers are made of a uniform elastomeric material.
Some of the following patent publications, which are more remote from the present invention, also deal with damping elements for surgical microscopes.
European Patent 1 248 133 B1 discloses a microscope stand having a vertical column and a horizontal support arm which is pivotable about the axis of the column of the stand. The means provided for vibration damping are in the form of a torsional damping element adapted to counteract torsional forces caused by horizontal pivoting movements of the support arm relative to the vertical column of the stand. This torsional damping element is kept free of axial forces and is loaded solely in shear.
In the context of surgical microscopes, Patent Publications DE 10 2006 044 469 A1 and US 2008 0 055 739 A1, as well as US 2008 0 058 109 A1, describe a drive motor driving a carriage, which in turn interacts with the zoom system of a surgical microscope. The drive shaft of the motor is connected to the carriage via an elastomeric damper.
German Patent Application DE 10 2008 011 311 A1 discloses a ceiling mount which also addresses the issue of vibration damping. In that patent, however, the problem of vibration damping is solved by a horizontally movable carriage. The movable carriage has associated therewith a mechanical end stop having a rubber buffer. However, the carriage of this known ceiling mount, too, has a vibration damping effect only for natural vibrations caused by movement of the microscope.
Thus, due to the large weight of the mount and the instrument suspended therefrom which, in total, may exceed 400 kg, conventional ceiling mounts have the disadvantage that vibrations, including both natural vibrations and vibrations of the ceiling, are not sufficiently damped. Typically, the microscope is mounted on the end of a usually multi-part support arm. A counterweight is provided to maintain the center of gravity of the overall system substantially below the ceiling attachment point. Moreover, an equipment box may be provided, either separately or as part of said counterweight, allowing basic settings to be made for the overall system. Thus, natural vibrations are involuntarily caused, on the one hand, by controlling or moving the microscope and/or the microscope support arm, and on the other hand by manipulation of the equipment box. The damping elements previously used in the arms may have been effective for vibrations originating at the microscope itself, but there has heretofore been no causal damping of vibrations originating at the control box. Moreover, previous designs were not effective for vibrations of the ceiling. In this context, ceiling vibrations are understood to include not only those mentioned above, but also vibrations which may be accidentally caused by equipment on the ceiling or in the room and introduced into the stand via the ceiling.
Although the prior art has provided various damping interfaces, there is still an enormous need for improvement since the high weight of the overall system and the resulting quantity of energy to be dissipated exceed the capabilities of known approaches. In addition, in particular, in operations which are performed under optical magnification to ensure pinpoint accuracy, such as in neurosurgery, eye surgery, etc., high accuracy is crucial for successful results. Regardless of their causes, unwanted vibrations can negatively affect the surgery and the surgeon's performance and ability to concentrate. This is particularly because vibrations may interfere with the sharpness and quality of the image, and may therefore place continued excessive strain on the surgeon's visual system.
It is an object of the present invention to overcome these disadvantages and to provide a ceiling mount which will efficiently suppress the above-mentioned vibrations, regardless of their causes. However, the complexity of construction and manufacture should not be increased over known ceiling mounts. Another object is to ensure long-term reliability.
The present invention achieves these objects by providing a ceiling mount of the above-mentioned type in which the separate damping layers have different elastic properties. The use of different materials, and thus different elastic properties, for the two damping layers tremendously improves the damping characteristics of ceiling mounts.
The two ceiling mount sections are decoupled from each other by the interface and are typically constructed as follows: The upper section is anchored to the ceiling by a ceiling attachment means of the ceiling mount and provides the support or housing for the interface, and thus for the damping layers. The support or housing includes two plates or disks of rigid material (steel, aluminum, etc.) adapted to compressively sandwich the system of damping layers and the bracket plate therebetween. The lower section, from which the support arms and the medical instrument are suspended, is rigidly joined to, or forms a unit with, the bracket plate which separates the two damping layers. In other words, two damping layers compressively hold the load-bearing bracket plate therebetween, so that the bracket plate is acted upon by damping material both from above and from below. Thus, the bracket plate carries the entire weight of the ceiling mount.
This ceiling mount design provides a kind of spring-mass system, in which the mass is constituted by the lower section and the microscope, which, together, are connected to the upper section by two springs, namely the two damping layers. The provision of different materials having different damping properties made it possible to increase the energy dissipation in the interface and to significantly reduce the effect of vibrations, regardless of their causes.
In a preferred embodiment, the material of the lower damping layer has a higher modulus of elasticity than the material of the upper damping layer. As a first consideration, it may be noted that the lower damping layer bears the large weight of the entire instrument and the support arms, and, therefore, is preferably somewhat more rigid, while the upper, softer damping layer does not carry any load, but merely presses resiliently against the bracket plate from above. In reality, the effect achievable by the present invention is a combined effect of the damping action of both damping layers. The contributions of the individual damping layers to the overall damping effect vary depending on the nature and spatial orientation of the vibration and its excitation frequency. This makes it possible to cover a wide spectrum of mechanical disturbances and to efficiently damp such disturbances. These disturbances include not only vibrations acting vertically on the damping layers, but also those acting in a horizontal direction, in which the bracket plate may possibly also be excited to vibrate. Consequently, it must be ensured that the bracket plate is movable in all spatial directions within the two damping layers without exceeding the elastic properties thereof. With this configuration, it is also possible to efficiently damp low frequencies, for example, in the range of 4-10 Hz. Frequencies in the range of the power grid frequency, i.e., 50 or 60 Hz, are also efficiently damped in this way.
Further preferred embodiments are indicated in the subclaims and will be described below in more detail with reference to the drawings, in which:
Damping interface 10, which is shown enlarged in
Bracket plate 14 defines the beginning of lower section 7 of the ceiling mount. That is, the lower section of ceiling mount 2 is rigidly joined to the bracket plate, forming a unit therewith. Non-damping bracket plate 14 is made of a rigid material, such as steel, aluminum, or other metal alloys. A skirt rigidly joined to non-damping bracket plate 14 extends through a, for example, circular opening in lower damping layer 15 and provides a mounting flange for connection with the support arm system.
Thus, damping element 10 of ceiling mount 2 has a sandwich configuration. This is shown more clearly in the exploded view of
As an alternative to this type of connection, it would, of course, also be possible to use a housing that completely encloses the sandwich structure. In such an embodiment, the damping layers may also be produced at a later stage using casting or foaming techniques. From a vibration standpoint, non-damping bracket plate 14 forms part of lower section 7 of the ceiling mount. Moreover, bracket plate 14 has a downwardly projecting extension 19 provided with mounting holes for attachment of further platforms, bracket members, support arms, etc.
What is essential to the present invention is that the two damping layers 13, 15 be made of different materials with different elastic properties. In a particularly preferred exemplary embodiment, the damping layers are made of polyurethane (PUR) elastomers having open and closed cells. In a particularly preferred embodiment, the upper disk (layer 13) was made from the elastomer Sylomer® SR 450, and the lower disk (layer 15) was made from the elastomer Sylomer® HD 500.
Sylomer® SR 450 is suitable for a static range of use up to about 0.45 N/mm2, the static modulus of elasticity in this range being between about 3 N/mm2 and 5 N/mm2. The dynamic range of use is up to about 0.7 N/mm2, the dynamic modulus of elasticity in this range assuming values between about 4.5 N/mm2 and 7 N/mm2 (at frequencies of about <20 Hz). The mechanical loss factor (the ratio of energy dissipation and deformation work per cycle) of Sylomer® SR 450 is about 0.11.
Sylomer® HD 500 is suitable for a static range of use up to about 0.5 N/mm2, the static modulus of elasticity in this range being between about 5 N/mm2 and 7 N/mm2. The dynamic range of use is up to about 0.7 N/mm2, the dynamic modulus of elasticity in this range assuming values between about 5 N/mm2 and 30 N/mm2 (at frequencies of <20 Hz). The mechanical loss factor of Sylomer® HD 500 is about 0.5.
All values given above and all the following values are understood to understood to be in accordance with DIN 53513 and apply for a form factor of about q=3. The form factor is a geometric measurement for the form of an elastomer bearing and is defined as the quotient of the loaded surface to the exterior housing surface of the bearing. Of course, this does not exclude the possibility of using layers having other form factors for the purposes of the present invention. For the purpose of comparison, corresponding elasticity-related values are to be adapted accordingly.
These and other suitable Sylomer® materials are available from the Getzner Werkstoffe Company in Burs, Austria.
Of course, the present invention is not limited to these materials and parameters. For example, good results were also obtained with parameters different from those mentioned above. Since the entire load of lower section 7 of ceiling mount 2 rests on the lower disk (layer 15) (which implies a greater preload), it has proven advantageous to use the material of higher modulus of elasticity there and not at the upper side of the bracket plate 14. Further optimization is possible when one of the two damping materials, especially the lower material which takes up the entire load, has a higher mechanical loss factor than the upper material.
Within the scope of the present invention, hardly any restrictions are imposed on the material properties since the optimum design of the damping interface is dependent on the weight and construction of the instrument and the support arms. However, for use with surgical microscopes, the following parameter ranges have been found to be preferable:
In the working range used, the material of upper damping layer 13 has a static modulus of elasticity between about 2 N/mm2 and 6 N/mm2, particularly preferably between about 3 N/mm2 and 5 N/mm2. The material of lower damping layer 15 has a static modulus of elasticity between about 4 N/mm2 and 10 N/mm2, particularly preferably between about 5 N/mm2 and 6 N/mm2.
In
The present invention is not limited to the exemplary embodiment shown herein. In contrast to
It is also conceivable to employ more than two damping layers. In this case, different materials having different elastic properties may alternate, it being preferable to provide a non-damping bracket plate therebetween respectively.
It is also within the scope of the present invention to attach the interface directly to the ceiling; i.e., without upper section 6.
Furthermore, in the context of the present invention, the term “ceiling” is understood to refer to all substantially horizontal structural elements of a building, including those which do not cover a room.
The ceiling 4 shown in
1, 1′ surgical microscope
2 ceiling mount
3 patient
4 ceiling
5 intermediate ceiling/suspended ceiling
6, 6′ upper load-bearing section
7, 7′ lower load-bearing section
8 support arm
8
a, b members of a support arm
9, 9′ articulation mechanism
10, 10′ damping interface
11 upper housing plate
12 lower housing plate
13 upper damping layer
14 bracket plate
15 lower damping layer
16 clamping bolt
17 O-ring
18, 18′ ceiling attachment means
19 downward extension
| Number | Date | Country | Kind |
|---|---|---|---|
| 0059/10 | Dec 2009 | CH | national |
| 10 2009 059 021.8 | Dec 2009 | DE | national |
